Acetylene is a colorless gas at atmospheric temperatures and pressures that burns in air with an intensely hot, luminous and smoky flame. Acetylene is used in a variety of applications, such as chemical synthesis, oxy-acetylene welding, cutting, heat treating and for lighting purposes in buoys, beacons and similar devices. Acetylene can be liquified and solidified relatively easily. However, in both the liquid and solid states, when ignited, acetylene may explode with extreme violence. Although acetylene is not explosive at ordinary atmospheric temperature, at two atmospheres or more it is explosive by spark or decomposition.
Acetylene is classified by the Department of Transportation as a flammable compressed gas, and must be shipped in steel cylinders manufactured to particular specifications. These specifications require, among other things, that the steel used in the cylinder meet certain chemical and physical requirements, and that the cylinder fillers have 92 percent or less porosity when charged with a specified amount of solvent, and be protected by adequate safety release devices.
Acetylene cylinders must avoid the decomposition characteristics of the gas by providing a porous mass packing material having minute cellular spaces so that no pockets of appreciable size remain where "free" acetylene in gaseous form can collect. Acetone dissolves 25 volumes of acetylene at 15.degree. C. and 760 mm, but 300 volumes at 12 atmospheres. Thus, the porous mass of acetylene cylinders is typically saturated with acetone or another solvent in which acetylene dissolves.
Previously known acetylene cylinders, when properly constructed and filled with porous material containing a suitable solvent, have safely avoided the hazard of high-pressure acetylene. In such conventional cylinders, asbestos fibers have commonly been used as a reinforcing agent for a hardened calcium silicate filler mass. Because of concerns posed by uses of asbestos fibers, attempts are being made to find a substitute for asbestos fibers in the calcium silicate fillers of acetylene storage vessels.
Thus, U.S. Pat. No. 4,349,463, inventor Flanigen issued Sept. 14, 1982, reissue filed May 22, 1985, discloses an acetylene storage vessel in which asbestos fibers have been replaced with alkali resistant glass fibers. These alkali resistant glass fibers are said to reinforce as well as function as suspending agent for the aqueous slurry from which the hardened silicate filler mass is manufactured. U.S. Pat. Nos. 4,467,040, inventors Brumi at al., issued Aug. 21, 1984 and 4,467,041, discloses the replacement of asbestos by utilizing amorphous, ultrafine synthetic silicas made by the pyrogeneation of silicon tetrachloride or chemical precipitation of the soluble silicate in an aqueous medium.
Because of the unique criteria for acetylene cylinder filler compositions, such as porosity, freedom from internal voids, little or no space between outer filler surface and inside walls of the containers, adequate strength and resilience, as well as manufacturing considerations and the safety requirements, attempts to replace asbestos fibers with other components have not been particularly successful and have not led to predictable results. Thus, for example, acetylene storage fillers made with fiberglass rather than asbestos fibers have been found to show some shrinkage and a considerable number of randomly oriented cracks. A filler made with cotton fiber rather than asbestos has been reported to contain many elongated pockets arranged in a herringbone pattern from the top to the bottom of the cylinder. Fillers dependent upon alkali resistant glass fibers as a reinforcing agent incur difficulties because the fibers do not fibrillate during mixing of slurries so that care must be taken to prevent overmixing. Many manmade fibers, such as polyester and rayon fibers, have been found to lead to a tendency of settling in the slurry during manufacture, which causes difficulties in obtaining the necessary composition uniformity when hardened within the cylinder. The addition of usual supplementary ingredients as suspending agents tends to decrease strength and porosity and adversely affects the acetylene discharge properties.
Accordingly, the need for new acetylene storage vessel fillers without asbestos fibers but with comparable performance to the prior fillers with asbestos remains.